With Wanganui having numerous earthquake-prone buildings, Ms Main was pleased with the extra five years to fix them.
However, she was concerned at the impact the cost of carrying out assessments would put on the district council - and ratepayers.
"Apparently, assessments will now be the responsibility of the council, but there's been no mention of the cost of that or of any financial assistance," she said.
"We will be keen to talk to the minister about what that will mean for us."
She said there were probably up to 500 buildings in the city that would still need assessing.
"If we estimate the cost of each to be around $3000, then we're looking at $1.5 million."
Richard Thompson, chair of Uncertainty of assessment costs on buildings
the earthquake prone buildings community taskforce, said he was concerned that under the new legislation, those building owners who had already had assessments done would not get the extra five years to fix their buildings.
Those owners will still be required to fix or pull down their buildings in the original time frame they were given. "This (gives an advantage to) people who were tardy, because they will get that extra five years," Mr Thompson said.
"Wanganui has been quick off the mark in getting assessments done, and it seems we're being penalised for it."
He said the taskforce would meet soon to discuss the proposed legislation.
Mark Simmonds, who co-owns an earthquake-prone building, said he didn't think the legislation would affect him much because the assessment on his building had shown it needed less work than was first thought. But he said the extra five years would give some Wanganui owners time to find more funds to fix their buildings.
"Unfortunately, I don't think it will be enough to save many of Wanganui's finest heritage buildings," Mr Simmonds said.
Meanwhile, councillor Michael Laws said the extra five years provision showed the Wanganui council had been hasty in its decision to relocate and strengthen the Sarjeant Gallery. "The cost of the temporary relocation will exceed $2 million," he said.
"Myself and other councillors said wait until the government announces its earthquake policy and today's announcement makes clear that we could have saved Wanganui ratepayers around $2m.
"A building that has never been damaged by earthquakes in over 90 years is now to lie vacant at significant cost."